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Old Jul 02, 2014, 08:39 AM
Registered User
United States, MI, Grand Ledge
Joined Jan 2013
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Covering a concave surface!

I am going to be covering a wing with a profile as shown below. Never done this before and my fears are becoming intense. Someone willing to lead me through this? On a full size aircraft, I might use ceconite and sew the fabric to the ribs. On this 4' wing I've been thinking silk and sewing. Possibly balsarite? I am leaning away from the heavier iron on monokote type plastics because of the vintage characteristics of the aircraft. Bright and shiny doesn't work on this plane.

Anyway, I sure could use a step by step on this. I don't want to develop any bad habits on my first attempt.

Thanks, Barry
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Old Jul 02, 2014, 09:54 AM
AndyKunz's Avatar
Illinois
Joined Sep 2001
22,095 Posts
Build a test wing!!!! You can make both sides concave, too.

What covering material are you going to use? It makes a difference to the prep material/technique, but you definitely will get better results prepping the wood first.

Andy
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Old Jul 02, 2014, 10:38 AM
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United Kingdom, England, Brighton
Joined Apr 2007
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There are several non-glossy vintage style coverings available (presumably in the US as well as the UK).

I've used Solartex on undercambered wings and it stayed stuck to the undercamber fine during shrinking. It's not glossy and has a very vintage look as it is a woven fabric with an adhesive backing. Fibafilm is similar and perhaps lighter. It doesn't have an adhesive backing, so you paint the airframe with Balsloc first, which is a heat-activated adhesive.

My J60 has undercambered wings and is covered in 'Linen' Solartex:

http://www.rcgroups.com/forums/attac...mentid=6181397

Some people prick the undercamber with a pin and use tiny drops of cyano to stick the covering to the rib before shrinking. Never tried it myself though.
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Old Jul 02, 2014, 12:27 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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I do it all the time given my love of old time free flight models.

The trick is to start from the middle line. If there's a spar that meets the lower surface you start with tacking the film or material down to the main spar. Then the next spar. Or if no second spar than on to the leading and trailing edges. Tend to pull spanwise with some tension but when laying it on the leading and trailing edges just let it lay smoothly with no chordwise tension. That'll give you a little slack for tacking to the rib curves. I actually find that most films, fabrics and tissue paper will simply lay smoothly into the arc of the ribs from there own weight. So no need to provide for additional slack. But something with as strong a hollow just behind the leading edge like you show might need a little extra help.

Then you start from the middle rib and start tacking the film down to each rib. Use a push and tack at this point so you don't pull the film.

Finally after it's all tacked down use a running ironing along the spars first, then leading and trailing edges and final along the ribs working out in either direction from the main spar. The running seal should be light for the first pass then a second pass with the iron pressed a little more firmly. This should avoid the film creeping.

Use a temperature and speed that softens the glue but doesn't make it liquefy and go slippery or you might end up with the film pushing. If that happens you sigh and pull it the other way. Then turn down the iron or move faster.

A patch of slippery fabric in your other hand is sometimes needed to press the film down on the ribs as you run the iron over the ribs. Otherwise the film can lift. But with a quick following slippery rub down it cools and sticks just fine.

If using a tissue or fabric and dope use a very little more chord wise slack. Work in the same order but in this case you don't tack the fabric down. You simply soak through with the thinner and then use your finger to rub the fabric to the rib or other part until it sticks.

Solvent absorption is a bad thing. Use nitrile gloves for this part to avoid skin contact.
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Old Jul 02, 2014, 12:53 PM
Registered User
United States, MI, Grand Ledge
Joined Jan 2013
115 Posts
The subject of this discussion is a 1910 Farman. It will be electric powered, so, I am leaning toward a fabric covering. DeeBee1's use of Solartex linen would be a wonderful candidate, especially since his attached photo gives me something to strive for. ....Nice work DeeBee1!

Though I have built many planes using silkspan and dope, with an electric I can get away with nitrate dope, not butyrate, so shrinkage should be less. What bothers me about paper, either silkspan or tissue, is the randomness of the knap. Silk should require less dope to give a decent finish. Yet, by the time I'm done with all that, wouldn't the Solartex come in with a comparable finish weight but with a faster turnaround time?

I will certainly take Andy's suggestion to heart and build up several trial "wings". I should be able to practice while the plane itself is being built, using the guideline suggested by Bruce.
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Old Jul 02, 2014, 06:24 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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I'd go for the solartex as well. Or since it comes with the glue already on the fabric it may be heavier than you want depending on the size of the model.

I recently picked up some light and shear 60%cotton/40%silk material. It's a trifle more dense than the classic silk stocking weave typically used on models. But as a result it would not be as transparent. The classic silk is too thin for a proper scale appearance. But I suspect that the Solartex is going to be too thick. Ideally it would be something in between that lets the light and shadows of the ribs show easily but which doesn't allow a direct through sort of translucent view like old time model silk with dope.
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Old Jul 02, 2014, 10:23 PM
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United States, KY, Taylorsville
Joined Mar 2010
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Here are examples of Koverall stuck down using... Stix-It! Fabric sealed with nitrate dope then butyrate applied. The strut braced sailplane, Balestruccio', has fabric sealed with hi-gloss polyurethane varnish! No dope was used on it. No rib stitching was used on any of these models.
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Old Jul 03, 2014, 02:23 AM
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BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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The Koverall looks GREAT! I'd call the amount of translucency you got with the fabric and clear dope just about perfect.
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Old Jul 03, 2014, 09:53 AM
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United Kingdom, England, Brighton
Joined Apr 2007
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The 'linen' Solatex is thicker than the other colours. The 'antique' colour is more translucent and should give something closer to ARUP's pictures. There are some images of model covered with antique solartex on Google.

As I mentioned, Fibafilm is lighter if weight is a concern as the adhesive is applied to the frame, not the covering.
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Old Jul 05, 2014, 09:09 AM
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Sonsight's Avatar
United States, AR, Cabot
Joined Aug 2004
106 Posts
I cheat. When I covered my 80" Playboy senior with Ultracote, I did the following. Seal the outer edges with a normal heat shrink iron. Then, (using a Top Flight trim iron) I would start at one end, and go bay to bay, gently pushing the covering down while I hit it with the trim iron. Each bay, from front to the rear of the rib. Do each bay like this. Then, once that is done, take the trim iron & shrink the covering in between the ribs. Don't use your heat gun here! Do this slowly, and take your time. Its easier than you think.
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Old Jul 06, 2014, 08:26 AM
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Joined Jun 2014
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Go to you tube and search for " Covering a wing with polyspan". The poster shows his technique for covering an under camber wing.
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